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Peer into the zebrafish at Naturalis; learn more about humans

At the National Natural History Museum Naturalis in Leiden it is now possible to magnify the larva of a zebrafish up to 500,000 times. This small fish is a popular research subject because it teaches us about the processes of illness and health in humans.

You can zoom in on the larva, a healthy one by the way, with a Cell Zoomer, an enormous touchscreen. ‘What the exhibition shows is that a zebrafish is very similar to us at the level of cells and molecules,’ says researcher Dr Annemarie Meijer from the Institute of Biology’s Molecular Cell Biology Group. She herself uses the zebrafish for her research into the defence against bacterial infections such as tuberculosis. Her colleagues are studying the fish to find answers to various questions relating to the growth and spread of cancer. Elsewhere in the Institute developmental biologists are studying how the larvae of the zebrafish reach maturity. This small tropical aquarium fish – measuring just 3 to 4 cm – is even popular in behavioural research.

The fact that the zebrafish embryos (larvae) are transparent makes it possible to study diverse processes in the living organism. With the aid of biotechnological techniques scientists have succeeded in linking the gene for a light-emitting protein to the genetic switches that activate genes. If a certain gene becomes active the light goes on in these cells. Meijer explains: ‘With different colour variants of the light-emitting protein we can, for example, get blood vessels to transmit green, defence cells red and bacteria blue light. You can then observe what is happening in the living fish under a fluorescence microscope.’

The basis for the interactive exhibition at Naturalis is an archive containing 30,000 electron microscope pictures of a zebrafish larva. There are pictures of the whole creature from head to tail. If we joined together the biggest enlargement of the larvae, in real life 1.5 millimetres in size, the images would cover the Malieveld park in The Hague twice over. The electron microscope group of Prof. Bram Koster of the LUMC signed up for the painstaking work of preparing the specimen, cutting it into ultra-thin slices and taking the photos.

The result is not just of aesthetic and educational value: it is also of scientific interest. According to Meijer, ‘Not only do we now know what a healthy fish looks like, we have an electron microscope atlas that can serve as a reference for studying processes of illness.’

Incidentally, the atlas, which can be found at the Museum’s Research in Progress Department, is already more or less ripe for revision. With the newest electron microscopes of the Netherlands Centre for Electron Nanoscopy (NeCEN), it is possible to delve even deeper into the molecules of each cell.

The initiative for the exhibition at Naturalis came from Cyttron II, the collaboration between knowledge institutions and businesses, of which the Leiden biophysical chemist Prof. Jan Pieter Abrahams is Scientific Director. In giving the public a unique look at the level of cells and organelles, the scientists hope to get across something of the fascination that the world of the smallest things of all can evoke.